The present invention relates to the treatment of olfactory nuisances and to the puri-fication of air, both in open environments and in confined spaces.
The deodorization of atmospheres is a complex problem which has still not been satisfactorily solved. The most effective method still consists of bulk renewal of air in confined spaces, with hourly flow rates of 3 to 5 times per hour in densely populated locations, this situation being aggravated by uncontrollable smoking of tobacco. The effects of this on individuals are known, the least serious of these effects being the impregnation of clothing, the skin and the hair, the most worrying being the effects on public health, and those which can be numerically assessed most immediately being the energy costs to renew the atmosphere, both in terms of heating in winter and airconditioning in summer.
It is known (see P. Pichat, articles of the Congres Eurodeur [Eurodour Congress] 97, Jun. 25-26, 1997, Paris) that titanium dioxide (TiO.sub.2) develops photocatalytic activity under the effect of ultraviolet radiation, which, in the presence of air, generates "O*" free radicals. These free radicals attack chemical compounds adsorbed onto the surface of the TiO.sub.2 and, by a sequence of chemical reactions involving atmospheric oxygen, degrade their organic carbon to the ultimate stage of CO.sub.2. This activity has been exploited for the destruction of olfactory nuisances in various air-purifying devices. However, this photocatalytic action of TiO.sub.2 relies on slow overall kinetics and the odours which it is desired to destroy disappear only after a certain delay period from the moment at which the treatment is started.
It is also known that undecylenic molecules (undecylenic acid, its salts and esters, undecylenyl alcohol, undecylenaldehyde and their immediate chemical derivatives)--referred to hereinbelow as "undecylenic derivatives"--develop a powerful anti-odour activity at low doses on organic substances perceived as being very unpleasant, for example the decomposition products of animal dejecta (see FR-A-2,655,878). This property has been applied for deodourizing cardboard and paper (see FR-A-2,742,663). However, problems of persistance of this activity arise with paper filters simply impregnated with undecylenic derivatives, the nauseating and charged gases which wash against them or cross them also abounding in fatty substances whose accumulation blocks the porosity of the filter and inhibits the molecules of undecylenic derivatives by drowning them in a greasy magma.